The mixing console amplifies, mixes, distributes, modifies the sound quality and processes the sound effects of multiple input signals. It is the heart of a sound system. The blood circulation of this heart directly affects the stability of the entire system.
1. Signal input
The input signal of the mixer is roughly divided into low-impedance microphone signal input and high-impedance line signal input. Each input can be regarded as a water pipe, that is, if a mixer has multiple signal inputs, it is as if water from multiple water pipes flows into the mixer for processing. The distinction between low resistance and high resistance can be seen as the difference in water pressure or water velocity. For example: the high-impedance input level is high, as if the water pressure is very high and the water flow is rapid, it is appropriate to directly input it into the pool of the mixer, and there is no need to add any links in the middle to adjust the water pressure and water flow rate; but The low-impedance input level is low, just like the water pressure is very low and the water flow is very slow. It is not suitable to directly input it into the pool of the mixer. It is necessary to add a pump to the large pool to give the low-impedance and low water pressure. It increases to increase the speed of the water flow, so the low-impedance input channel of the mixer has a built-in special circuit amplifier to amplify the low level to an appropriate level. The characteristics of using water to describe low-impedance signals and high-impedance signals should be well understood by everyone.
2. Channel gain adjustment
To input the sound source into the mixer, we must first distinguish whether it is low-impedance or high-impedance, and then connect it to the mixer correctly with a standard signal cable. If you want to achieve perfect sound quality for each audio source, you need to adjust it carefully. The gain of each input channel of the mixer is very important and critical, but many sound engineers seem to treat the gain as simply a volume knob, which is quite wrong. In fact, the gain is mainly used to control the dynamic range of the input signal. Generally, the maximum effective dynamic range is when the gain is adjusted to the maximum without distortion, and it is also the best effect state. This is more difficult to understand, but it is better to describe it with water: the input channels and input lines of the mixer will have a basic background noise. This background noise is like the sediment in the river bottom, and it is inevitable. Everyone knows that when the river is not deep, the flowing water is under the mud and sand. The quality of such water is definitely not good. So in other words, if the dynamic range of gain adjustment is insufficient, the sound source signal is like flowing water under the mud and sand, and the background noise will emerge. The sound quality at this time is definitely not good; on the contrary, when the river is deep, The flowing water is relatively clear, and the water quality must be very good, that is to say, the dynamic range of the gain adjustment is larger and more reasonable, so the sound quality must be very good; of course, if the water is huge, even the dam will be washed down, and the river bottom will be given. If it is overturned, this is equivalent to the level signal is too large to be distorted. At this time, there is no sound quality, and it will also cause damage to the equipment. Therefore, the gain is not as large as possible, and it must be moderate and appropriate. The author would like to describe the effect of gain in this way, even audio beginners should be able to understand it.
3. Adjustment of channel equalization group
After the gain is adjusted, the next step is to adjust the equalization group of the mixer channel. The order of adjustment should be the bass part first, and then the mid-treble part. Because only the basic sound of the sound can be guaranteed to have good multiple overtones. Basic adjustments are okay for everyone, here I only talk about a few technical aspects.
Nowadays, the equalization groups of professional mixers generally have frequency selection adjustments. Many sound engineers do not use them flexibly. It is difficult to explain all of them in detail. Some things depend on personal savvy. I can only simply say: For example: It is said that when playing disco music, I feel that the bass is not strong enough. You can select the bass frequency of the channel equalization group where the disco music is located at about 200Hz, and then use the adjustment knob to moderately increase the bass power; for example, When the tooth tone of a female singer is obvious and prominent, you can choose the high frequency frequency around 6000Hz, and then use the adjustment knob to moderately attenuate the tooth tone, which will reduce the tooth tone appropriately. If you use it flexibly, you can also use the frequency selection function of the equalization group to suppress the acoustic feedback. For example, there is a formant around 300 Hz in a general dance hall. This frequency is often prone to acoustic feedback. You can choose the frequency of the microphone input channel at about 300 Hz. , And then use the adjustment knob to moderate attenuation, so that you can effectively reduce the acoustic feedback. Of course, the frequency of acoustic feedback generated by each sound field is different, but no matter what frequency the acoustic feedback is, it can be simply controlled by this method. Of course, this needs to be controlled flexibly based on experience, and the sound field must be perfectly adjusted and avoided. Acoustic feedback needs to be adjusted with a professional multi-band equalizer or feedback suppressor.
A mixer needs to be adjusted by the sound engineer frequently is the equalization group of the mixer. I often see that some sound engineers only know how to push and pull the volume fader, and are too lazy or do not know how to adjust the equalization knob. In fact, in use, it can be said that the mixer needs to be adjusted all the time.
Take a song as an example: When a singer walks to the stage to introduce his performance, he needs to turn down the bass of the microphone and adjust the reverberation to moderate or turn off, so that the clarity of the language can be guaranteed; when the music is played by the singer When you start singing, you need to increase the microphone bass, otherwise the sound will appear thin, and at the same time increase the reverberation volume to a suitable level; in addition, in order to avoid the music treble grabbing the microphone treble, you can slightly attenuate the music treble; When playing, the audience’s attention will shift from the singer to the music, so you need to increase the treble of the music at this time, and at the same time make the music sound louder, so that it will highlight the music very well and naturally, otherwise No change will appear too rigid. At this time, the reverberation volume should also be turned down, so that even if the singer suddenly speaks during the interlude, there will be no noise; when the interlude of the song is over and the next segment is sung, turn off the music. , Attenuate music treble, increase microphone and reverb volume. At the climax of the final singing, you need to turn the microphone volume up, and then turn on the music volume from low to high in an instant, to create a perfect, shocking, and magnificent climax effect for the ending. Of course not all songs are suitable for this The operation, so what you need to be a sound engineer is flexibility.
4. Channel AUX adjustment
The various adjustment knobs on the mixer are generally the most balanced group, followed by the AUX knob, the term is called: auxiliary send control. Due to its auxiliary nature, many sound engineers did not pay enough attention to it and did not fully understand its function. I remember that when I was studying at the Beijing Ministry of Radio, Film and Television in 1997, I talked about this AUX teacher for two days, but many students were still confused. In the end, the author really couldn’t help it. It took two minutes to solve their two-day confusion. After understanding, many students were lamenting that this AUX was so simple! Of course, I can’t say that the level of the author was higher than that at that time. Teacher, it’s just that the author used a vivid analogy: I said that in fact, each input channel of the mixer is like a big water pipe. After the water flows in, it is basically divided into two main water pipes, A and B, and a total of A road. The water pipe is: the volume fader of this channel of the mixer is sent out through grouping, etc. Everyone knows the volume fader of the channel; the other B-way main water pipe is: the AUX group, the difference is a mixer The AUX part can be divided into multiple channels. If a mixer has 4 channels of AUX, it is like dividing the AUX group’s B channel main water pipe into 4 channels of small water pipes and then flow out, it and the lower fader The principle is the same, except that most of the AUX volume switches are controlled by knobs, and the channel volume switches of the same channel are controlled by faders, just like a big water pipe, even if it is divided into two main pipes, A and B. , And there are many small water pipes under them, but the quality of the water flowing out is still the same. So we can't just look at the superficial differences of things. In fact, their functions are similar. Seeing this, most audio beginners should be able to understand it. The most important thing is to understand that the knob of AUX is actually the same as the volume fader of the mixer.
Next, I will talk about the specific usage of the AUX group: Generally, AUX is used to connect the vocal effector at most. The sound that needs to be processed is sent to the effector with the corresponding AUX switch, and then flows back to the effector after processing. Tuning, this is the basic knowledge, most sound engineers should know it. The AUX of a large mixing console generally has pre/post fader conversion. When set before the fader, the total volume fader under this channel cannot control the volume of this AUX; on the contrary, it is affected by the total volume of this channel. Volume control. Some other functions of AUX are for monitoring or recording. Another convenient use is that readers can also use AUX to control the bass volume of a sound system, so that if more bass channels are needed, the corresponding AUX can be opened up, without the need for large bass volume sound sources, such as microphones, etc. The corresponding AUX can reduce the volume, otherwise it is easy to produce bass feedback. If you understand the principle of AUX in general, you can draw inferences about it. I won't say much here.
5. Sound and image balance adjustment
The sound image of a mixer is generally understood by sound engineers, but many of them are rigidly understood. For example, if a two-channel stereo music signal is input to the mixer, most sound engineers will turn the sound and image knobs of these two channels to the mixer. Turn left and right to the end, thinking that this is "stereo". In fact, the sound from these two channels will appear to be very floating, and the middle will be faint and weak; if you turn the panning knobs all the way to the middle, you will feel that the music sounds are all It’s uncomfortable, and the width of the sound is not enough; the best position is that the panning knob of the left channel is turned to the 9 o'clock position of the clock, and the panning knob of the right channel is turned to the 15 o’clock position of the clock. The music will not flutter, the dynamic range is wide, and the intensity and penetration are good. You can try it carefully, the author will not analyze the principle, the author only focuses on practice. I won't say much about other aspects of audio and video applications, they are all basic knowledge. In fact, it is often considered the simplest thing, but it is very complicated when you think about it.
6. Adjustment of the main output part
The main output part of the mixer refers to the group volume and the total volume. For example, you can organize the band into 1-2 groups; organize the microphones into 3-4 groups; control the bass through the volume of the 5-6 group, and control the auxiliary speakers through the volume of the 7-8 group. In short, there are multiple Grouped mixers are better and easier to control. In addition, the group can choose to output the signal separately or switch the group signal to the master volume mixing control of the mixer. Others such as channel faders are very simple, but the volume faders should be flexibly controlled according to the situation of each input channel. Although the adjustment of this part is simple but very important, the main thing is to observe the input and output levels of each signal. The signal must not be severely distorted.
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